Tiered control architecture for material handling

ABSTRACT

A control architecture for material handling includes multiple tiers of controllers, such as three. The lowest-level controllers interact directly with sensors and actuators used in the material handling system, such as photo-eyes and motors used with conveyors. The lowest-level controllers receive higher level commands from one or more mid-level controllers. The mid-level controllers, in turn, receive still higher level commands and information from at least one upper level controller. Each mid and low level controller is designed to include sufficient intelligence to deal with many of the signals and messages it receives without having to forward those signals or messages to the next higher level controller and await instructions from that higher level controller. The system thus distributes intelligence amongst the controllers. The system is well-adapted for application to conveyor control systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/162,580, filed Sep. 15, 2005 which claims priority to U.S. patentapplication Ser. No. 10/163,788, filed on Jun. 6, 2002, which, in turn,claims the benefit of U.S. provisional application Ser. No. 60/296,628,filed on Jun. 7, 2001, all of the foregoing disclosures of which arehereby incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention generally relates to control systems, and moreparticularly to the architecture of a control system for controllingmaterial handling operations.

Automated material handling systems are available in a wide variety offorms, such as conveyor systems, automatic guided vehicles, electrifiedmonorails, automatic storage and retrieval systems, and others. In thepast, these types of material handling systems have been controlled bycontrol systems having generally one of two different types ofarchitecture. In one architecture, each of the sensors and actuators inthe system is directly connected to a central controller. For example,in a conveyor system, the motor controllers that control the conveyors,along with the photo eyes that sense articles being carried on theconveyor, would all have direct wire connections to the centralcontroller. In a second type of control architecture, a centralcontroller is directly connected to each and every actuator or sensor inthe material handling system via a network or other type of system thatuses shared communication channels. While this latter type of system hasthe advantage over the former system in that it reduces the wiringnecessary to implement the system, both systems have their drawbacks. Inparticular, both systems require the central controller to deal witheach and every actuator and sensor in the system. This may severely taxthe capabilities of the central controller, requiring it to prioritizemessages and delay certain responses. Additionally, such systems may bedifficult to scale to different sizes when implemented. For example, acentral controller that can accommodate 10 inputs and outputs may not becapable of accommodating 100 or even 1000 inputs and outputs withoutredesigning the entire central controller. Past systems that have usedshared communication channels have also required high bandwidths inorder to accommodate all the necessary communication.

Accordingly, the desirability of a material handling control system thatovercomes these and other disadvantages can be seen.

SUMMARY OF THE INVENTION

The present invention substantially overcomes the above-noteddisadvantages and provides a material handling control systemarchitecture that is highly modularized, scalable, and easier toimplement and repair than prior systems.

According to one aspect of the present invention, a control system forcontrolling one or more conveyors having at least one sensor for sensinginformation about the conveyors, and at least one actuator forcontrolling one or more aspects of the conveyors is provided. Thecontrol system includes at least one low-level controller that receivessignals from the sensor and outputs commands to the actuator. Amid-level controller is also provided that receives status informationfrom the low-level controller and outputs commands to the low-levelcontroller. A high level controller is also provided which receivesstatus information from the mid-level controller and outputs commandsback to the mid-level controller. The commands are at least partiallybased on the status information.

According to another aspect of the invention, a conveyor sortationsystem is provided that includes at least one sensor, a sortation bed, aplurality of pushers, at least one diverter switch, and a first and asecond controller. The sortation bed includes a plurality of generallyparallel slats that define a conveying surface that carries articles tobe sorted. The slats move in a direction of conveyance. The pushers aremovably coupled to the slats in a direction generally transverse to thedirection of conveyance. The first controller is in communication withthe sensor and the divert switch and is adapted to issue a command tothe divert switch and to determine if the divert switch successfullycarried out the command. The second controller is in communication withthe first controller and receives a message from the first controller ifthe command is not successfully carried out.

According to another aspect of the invention, a method of controlling aconveyor sortation system is provided that includes providing asortation bed, a first controller, a second controller, and a pluralityof third controllers. The sortation bed includes a conveying surfacemovable in a direction of conveyance. The first controller is adapted todetermine an article's intended destination. The second controller isadapted to determine an article's position on the conveying surface. Thethird controllers control a plurality of associated divert switches thatare used for selectively diverting articles off of the sortation bed. Anarticle's intended destination is sent from the first controller to thesecond controller and one of the plurality of third controllers isselected based on the article's intended destination. Thereafter, anarticle's location on the conveying surface is sent from the secondcontroller to the selected third controller and the selected thirdcontroller is instructed to divert the article when the location reachesthe associated divert switch.

According to yet another aspect of the present invention, a conveyorsortation system is provided that includes a sortation bed having aplurality of generally parallel slats that define a conveying surfacethat carries articles to be sorted. The slats are movable in a directionof conveyance. The system further includes a detectable element, aplurality of pushers and switches, a sensor, and a switch controller.The detectable element is coupled to at least one of the slats thatidentifies the slat. The pushers are movably coupled to the slats andmovable along the slats in a direction generally transverse to thedirection of conveyance. The switches are capable of selectivelyassuming a diverting state in which the switches cause at least one ofthe pushers to move in the generally transverse direction. The sensordetects the detectable element and the switch controller activates oneor more of the switches into the diverting state based at leastpartially on when the sensor detects the detectable element.

The present invention focuses each level of the system at progressivelyhigher levels of abstraction in the material handling control scheme.Progressing from a pure sensor and actuator focus, up to individualpackets of material being moved and finally to overall streams ofmaterial in the system. This provides for greater isolation ofconflicting functionality such as user interface and hard real-timecontrol, thus making the design of each level simpler and easier to bothdevelop and incorporate new technologies as they become available. Thepresent invention may advantageously be applied to conveyor materialhandling systems, including conveyor sortation systems.

As noted above, the present invention provides improvements in materialhandling control systems, such as scalability, cost, repair, andsimplicity. These and other benefits, results, and objects of thepresent invention will be apparent to one skilled in the art in light ofthe following specification when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a conveyor control system according to oneaspect of the present invention;

FIG. 2 is a block diagram illustrating the control architectureaccording to one aspect of the present invention;

FIG. 3 is a block diagram illustrating one embodiment of a controlsystem of the present invention;

FIG. 4 is a perspective view of a sortation conveyor bed which may beused in conjunction with the present invention;

FIG. 5 is a perspective view of a shoe and slat that may be used withthe conveyor of FIG. 4;

FIG. 6 is a side, elevational view of the diverter shoe of FIG. 5;

FIG. 7 is a plan schematic view of the sortation bed of FIG. 4illustrating several branch conveyors and control structures;

FIG. 8 is a perspective view of a divert mechanism usable with thesortation bed of FIG. 4;

FIG. 9 is a schematic view of the sortation bed of FIG. 4 illustratedwith a speed control system;

FIG. 10 is a schematic view of a control architecture according to oneaspect of the invention;

FIG. 11 is a schematic view of another control architecture of thepresent invention;

FIG. 12 is a schematic view of still another control architecture of thepresent invention; and

FIG. 13 is a diagram of a divert command.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described with reference to theaccompanying drawings wherein like reference numerals correspond to likeelements in the several drawings. An illustrative example of a tieredcontrol system 20 according to one aspect of the present invention isdepicted in FIGS. 1 and 2. Control system 20 is depicted for use inconjunction with a conveyor system 22. While tiered control system 20can be used for controlling material handling systems other thanconveyor systems, a conveyor system will be used herein for purposes ofdescription and it should be understood that, unless otherwisespecified, the term conveyor is intended to cover all such systems. Forexample, it will be understood that tiered control system 20 could beused to control other conveyor systems including electrified monorails,automatic storage and retrieval systems, automated guided vehicles,combinations thereof, and other sorts of material handling operations inaddition to conveyor systems. Although the invention is illustrated witha conveyor system having a type of linear sorter, namely a positivedisplacement shoe and slat sorter, it could be used with conveyorsystems having other types of linear sorters or non-linear sorters.Examples of non-linear sorters include carousel sorters, such ascross-belt, tilt tray sorters and the like. It will also be understoodthat while the preferred embodiment depicts the tiers residing inphysically separate modules in conveyor system 22, this physicalseparation is not a necessary aspect of the present invention.

Conveyor system 22 includes an induction subsystem including one or moreinduct conveyors. Illustrated are a first induct conveyor 24 a andsecond induct conveyor 24 b which carry packages or other articles ontheir top surface in the direction indicated by the arrow (FIG. 1).Induct conveyors 24 a and b feed into a merge conveyor 26 which mergesthe articles on induct conveyors 24 a and b into a single conveyor 28.However, a single line induct of the type disclosed in commonly assignU.S. patent application Ser. No. 09/669,170 filed Sep. 25, 2000 byAffaticati et al. for a HIGH RATE INDUCTION SYSTEM, the disclosure ofwhich is hereby incorporated herein by reference may be used. Thecontrol of the induction and gapping of articles may use the techniquesdisclosed in commonly assigned U.S. patent application Ser. No.09/851,021, filed May 8, 2001 entitled CONVEYOR INDUCT SYSTEM, thedisclosure of which is incorporated herein by reference. Single conveyor28 carries the articles to a number or sortation stations 30 whichselectively sort the articles onto a plurality of branch conveyors 32.The precise mechanism for sorting articles onto branch conveyors 32 canvary substantially within the scope of the present invention. Thesortation equipment described herein is for illustration purposes andutilizes a plurality of shoes or pushers that move transversely acrossconveyor 28 in sortation stations 30 (See FIG. 4.). These shoes may beof the kind disclosed in commonly assigned U.S. Pat. No. 5,127,510issued to Cotter et al. or commonly assigned U.S. patent applicationSer. No. 09/968,743 filed Sep. 28, 2001, both of the disclosures ofwhich are hereby incorporated herein by reference. Alternatively, theshoes may be of the type depicted herein in FIGS. 4 and 5. Still othertypes of shoes can be used within the scope of the invention, as well asother types of diverting structures. In the embodiment of FIG. 1, eachsortation system 30 includes four guide tracks 34 which are positionedunderneath the conveying surface of conveyor 28. As described morebelow, guide tracks 34 cause the shoes on conveyor 28 to slidetransversely across the conveying surface when a divert actuator isactuated for a respective guide track 34. Conveyor 28 may furtherinclude a scanning station 38 located upstream of sortation stations 30.Scanning station 38 may comprise one or more photo eyes, cameras, orother devices for automatically determining the intended destination forpackages, or other articles, that are being conveyed by conveyor 28.Scanning station 38 may also be configured to measure the dimensionsand/or orientation of articles that are being conveyed on conveyor 28.

Packages or articles entering conveyor system 22 thus enter the systemillustrated in FIG. 1 on either induct conveyor 24 a or 24 b. Inductconveyors 24 a and b may be controlled in order to provide propergapping between packages as they are merged together on merge conveyor26. After being merged, the packages or articles travel on conveyor 28through scanning station 38. Scanning station 38 may read the barcodesor other means which are affixed to each of the articles to determinethe proper sorting of each of the articles. Alternatively, the intendeddestination of articles may be determined in a location upstream ofscanning station 38 and scanning station 38 may simply determine anarticle's precise location on the conveying surface of sortation system30. In addition to the article's precise location, scanning station 38may also measure the article's length and/or width. A plurality ofbranch conveyors 32 follow scanning station 38. Based on the intendeddestination of a particular article, it is diverted at the appropriatesortation station 30 onto the appropriate branch conveyor 32. Tieredcontrol system 20 controls all of the operations necessary for movingthe articles from induct conveyors 24 to sortation conveyors 32. Tieredcontrol system 20 is depicted schematically in FIG. 2 and describedfurther below.

Tiered control system 20, in the illustrated embodiment, includes threetiers of controllers. It will be understood that the present inventionfinds equal applicability to tiered control systems that include two ormore tiers of controls. As illustrated in FIG. 2, tiered control system20 includes one or more first tier controllers 44 a, b, and c, one ormore second tier controllers 42 a and b, and one or more third tiercontrollers 40. Each first tier controller 44 is in communication withone or more sensors or actuators 46 that are used in conveyor system 22.The sensors or actuators 46 may include photo eyes for detecting thepresence or absence of articles traveling on conveyor system 22, speedor rotation sensors for detecting the speed of conveyor motors, camerasfor determining information about the articles traveling on conveyorsystem 22, bar code readers for scanning barcodes affixed to thetraveling articles, Hall effect sensors for detecting changes inmagnetic flux, or any other types of sensors which may be employed in aconveyor system. Sensors/actuators 46 may also include motors, divertswitches for diverting shoes, and any other type of actuator which maybe used in a conveyor system. In the embodiment depicted in FIG. 1,sensors/actuators 46 would include photo eyes 48 and 104, slat sensors50 and 98, and a plurality of motors for powering each of the individualconveyors in conveyor system 22 (not shown). The sensors/actuators 46are in communication with one of the first tier controllers 44 a-c. Thecommunication may be by any known communication protocol and may includedirect links between each sensor/actuator 46 and the first tiercontroller 44 such as is illustrated with controller 44 a (FIG. 2).Alternatively, the first tier controller 44 may have a singlecommunications input and output which branches to each of the connectedsensors/actuators 46 such as is illustrated for first tier controller 44b. As yet another variation, first tier controller 44 may include a mixof direct links to sensors/actuators 46 and branching links, such as isillustrated with respect to first tier controller 44 c. In theembodiment depicted in FIG. 2, each first tier controller 44 is incommunication with three sensors/actuators 46. It will, of course, beunderstood that the number of sensors/actuators 46 with which each firsttier controller is in communication can be varied as desired. Also, thenumber of first tier controllers 44 can be varied from that depicted inFIG. 2, as well as the number of second tier controllers 42.

A slat sensor 50 is positioned upstream of the branch conveyors 32. Slatsensor 50 is preferably a device incorporating both an inductiveproximity sensor that detects the aluminum slats that define thesortation conveying surface and a Hall effect sensor to detect embeddedmagnetic fields in the slats to allow flexible differentiation of slats,as will be described more below. This allows a single sensor to providefor speed sensing, slat position sensing and unique slat identification.This latter feature allows the low level controllers 52 to simply reactto a particular slat by appropriate actuation of switches to initiate adivert without the need for precise timing information from the tier twocontroller 64 which is managing the sortation of individual packages. Anexample of slat sensor 50 is disclosed in published International PatentApplication No. 02/26602A2 published Apr. 4, 2002, the disclosure ofwhich is hereby incorporated herein by reference.

In this way, each first tier controller 44 can be primarily responsiblefor the detailed communications and controls for each of the connectedsensors/actuators 46. Each first tier controller may comprise aprocessor circuit board, such as a simple 8-bit microprocessor board,although other variations are possible. Each first tier controller maybe custom designed to perform a very specific set of tasks and they mayhave little or no human/machine interface. Examples of first tiercontrollers 44 depicted in FIG. 1 include divert control modules 52,motor control modules 54, and gapping control modules 56. Divert controlmodule 52 is responsible for selectively diverting the shoes that movetransversely across the conveying surface in sortation stations 30.Divert control module 52 communicates with actuators 46 which, in thiscase, are switches. The switches may be of a mechanical orelectromagnetic type, or some combination thereof. An example ofactuator 46 is disclosed in published International Patent ApplicationNo. 01/83342A1 published Nov. 8, 2001, the disclosure of which is herebyincorporated herein by reference. If the diverting of articles ontobranch conveyors 32 is to be carried out by means other thantransversely moving shoes, divert control module 52 would be incommunication with the actuators used for carrying out this type ofdivert.

Motor control modules 54 control a plurality of motors 58, which may belinear induction motors, or conventional rotating motors, and which areused to power the conveying surface of the conveyor. The linearinduction motors 58 therefore may power slats, bars, or other means forcarrying articles. A gapping control module 56 controls one or more ofthe motors that power the various belts of one or more sections ofinduct conveyors 24 a and b. Each gapping control module 56 controls thespeed and acceleration of induct conveyors 24 a and b in order to assignproper gapping distances between each of the articles traveling on theconveyor according to the speed schedule determined by the gap manager60. In the illustrated embodiment, gapping control module 56 does notdetermine or sense the desired gaps between the articles, thatinformation is provided from a second tier controller, such as gapmanager 60. Gap manager 60 supplies actuator/servo sequences, such asones that are generated in response to inputs from photoeyes, encodersor other sensors.

Each of the first tier controllers 44 communicates with one or moresecond tier controllers 42. The communication may be accomplished by anyknown means, such as peer to peer field bus communications. Examples ofbus systems that can be used include CAN bus, ASI bus, profibus,Bluetooth, and others. The communication may include either statusinformation or commands between the first tier and second tiercontrollers. By using field bus communications, the processors in thefirst tier and second tier controllers are not required to direct thecommunication between the two systems. The communications take placeusing defined types of messages, each having a pre-defined format. Byusing only defined messages with pre-defined formats, the specific typesof first and second tier controllers in any given system can easily bereplaced or upgraded without having to replace all of the other higheror lower tier controllers. The first tier controllers generally operatesubstantially in real time. For example, they may sense changes in theirinputs at high rates, such as within ten milliseconds or less, althoughother rates can be used within the present invention.

Second tier controllers 42 may include such controllers as gap managers60 and divert manager 62. These second tier controllers may use a higherlevel, commercial off-the-shelf processor board such as an X-86 classboard. Other types of processor boards are, of course, possible. Thesecond tier controllers are designed to do soft, real time processing orembedded processing. The second tier controllers know about the task ofthe specific subsystem (e.g., first tier controller or controllers) anduse the subsystem capabilities to execute tasks assigned to the secondtier controllers by the third tier controller. The second tiercontrollers 42 have limited, if any, human/machine interface.

Second tier controllers 42 are aware of individual cartons and theirposition, and issue appropriate commands to their respective first tiercontrollers. The first tier controllers, on the other hand, do notmaintain information on the position of the cartons or other types ofarticles, but rather follow the instructions received from the secondtier controller. For example, divert manager 62 maintains information oncarton position, which diverts are associated with which groups ofbranch conveyors 32, which sortation stations 30 may have less than alltheir diverting shoes operable and the like. On the other hand, divertmanager 62 would not issue commands directly to motors to control thesortation bed speed or to switches to divert articles. Instead, secondtier controller 42 issues higher level commands to tier one controllers,such as the amount of propulsion that should be exerted to propel thesortation bed, or the specific slats that should have their associatedpushers diverted. The tier one controllers interpret these commands andissue appropriate control signals that power the attached motors orswitches in a manner that will effect the higher level command from thetier two controller. The tier one controllers thus include intelligenceabout the specific signals that are needed to control their attachedactuators, as well as sufficient intelligence to convert the high leveltier two commands into the appropriate control signals to be output tothe actuators.

Third tier controllers 40 are the highest level controllers in tieredcontrol system 20. Third tier controllers 40 are dedicated to plantinterface and system wide control and decision making. At this level,details of how cartons are sorted, inducted, identified and the like arenot directly controllable. Third tier controller 40 is concerned withthe carton flow and routing, plant interface, central diagnostics, andfault reporting, system start up/shut down control and the like. Thirdtier controllers 40 are not necessarily real time or soft real timeprocessors.

Third tier controller 40 may use conventional, off-the-shelf microcomputer hardware at the Pentium® class level. Other types of hardwaremay, of course, be used. Third tier controller 40 has significantcommunications and human/machine interface capabilities. It may also bea node on a plant wide network or on a global network, such as theInternet. Third tier controller 40 generally does not concern itselfwith cartons as individual entities but rather controls streams ofcartons and information flow broadly.

It will of course be understood by those skilled in the art that tieredcontrol system 20 has applications to systems other than that depictedFIG. 1. For example, FIG. 1 depicts multiple first and second tiercontrollers. It would also be possible to implement tiered controlsystem 20 for a single portion of a conveyor system 22. For example,tiered control system 20 could be implemented primarily for thediverting aspects of a conveyor system. An example of such a system isdescribed below.

A control system 70 specifically tailored to a conveyor sortation systemis depicted in FIG. 3. Control system 70 is but one specific applicationof a tiered control system 20. Control system 70 is used to control aconveyor sortation system, such as one comprised of the various partsand components depicted in FIGS. 4-9. Control system 70 is a threetiered control system. It includes a tier three system controller 40; adivert manager 62, which is a tier two controller; and a plurality oftier one controllers. In this particular embodiment of control system70, the tier one controllers come in two different types: divert controlmodules 52 and motor control modules 54. Divert control modules 52control the diverting movement of a plurality of shoes or pushers 72 ona sortation bed 74 in a manner which will be described in more detailbelow. (See FIG. 4). Motor control modules 54 control the speed of thesortation bed 74. With specific reference to FIG. 4, motor controlmodules 54 control the speed at which a conveying surface 76 moves inthe direction indicated by arrow 78. The operation of controllers 40,52, 54, and 62 will now be described with reference to the conveyorsortation system and its components depicted in FIGS. 4-9.

The construction and operation of sortation bed 74 is described morefully in commonly assigned, U.S. Provisional Patent Application Ser.Nos. 60/236,230 and 60/278,892, filed on Sep. 28, 2000 and Mar. 26,2001, respectively. The construction and operation of sortation bed 74is also described more fully in International Publication No. WO02/26602 A2. The entire disclosure of all three of these applications ishereby incorporated herein by reference. It should be understood thatsortation bed 74 is but one example of an environment in which controlsystem 70 can be applied, and is set forth in detail herein to morefully understand the application of control system 70. In general,sortation bed 74 includes a plurality of slats 80 which areinterconnected with each other to form an endless loop, the top surfaceof which defines conveying surface 76. Slats 80 are powered by linearmotors that cause them to move in the direction indicated by arrow 78.Articles 82, such as packages or other items to be conveyed, are carriedon the conveying surface 76. A plurality of branch conveyors 32 arepositioned along either side of sortation bed 74, such as depicted inFIG. 7. When conveying surface 76 has moved an article 82 to a positiongenerally adjacent a branch conveyor 32 that leads to the article'sintended destination, the article is automatically pushed off ofsortation bed 74 onto the correct branch conveyor 32.

The articles are pushed off of sortation bed 74 by way of the pushers72. Each pusher 72 is movable along the length of its associated slat 80in a direction perpendicular to the direction of movement 78 ofconveying surface 76. This direction of movement is indicated by arrow84 in FIG. 5. Each pusher 72 includes a downwardly depending pin 86 towhich is attached a transfer assembly 88. Transfer assembly 88 is anelongated member utilized to divert the pusher 72 along a particularguide rail or track 34 which thereby causes the pusher to move generallytransversely across conveying surface 76. A transfer assembly 88 isdepicted in FIG. 8 without its attached pusher for purposes of clarity.When a pusher 72 is not being used to push an article off of conveyingsurface 76, transfer assembly 88 travels in a channel 90 defined alongone side of conveying surface 76. Channel 90 is oriented generallyparallel to the direction of conveyance 78. A pusher 72 whose transferassembly 88 is traveling in channel 90 therefore stays along one side ofits associated slat and does not divert any articles off of sortationbed 74.

When an article is to be diverted to a particular branch conveyor 32,guide tracks 34 and switches 92 are used. In the illustrated embodiment,there are four guide tracks 34 positioned adjacent each branch conveyor32. It will be understood that the present invention finds applicationto systems with only a single guide track adjacent each branch conveyor,or to systems with still other numbers of guide tracks 32. When a pusher72 is to be diverted to move longitudinally along the length of its slat80 (i.e. transversely to the direction of conveyance 78), a selectedswitch 72 is activated. In the illustrated embodiment, switches 72 areelectromagnetic switches and transfer assemblies 88 include magneticportions that are attracted to electromagnetic switches 72 whenenergized. This attraction diverts the transfer assembly 88 out ofchannel 90 into a divert path 94 adjacent the energized electromagneticswitch 92. The divert path 94 is defined adjacent a divert rail or guidetrack 34 associated with that particular electromagnetic switch 92.Because the guide tracks 34 are angled with respect to the direction ofconveyance 78, the transfer assembly 88 is pushed in a direction havinga motion component that is transverse to the conveyance direction 78.This movement causes the pusher 72 to move along its associated slat andthereby push against an article that is on the slat. By selectingparticular ones of switches 92 to activate, as well as particularlengths of times for them to be activated, different numbers of shoes 72can be diverted to cause an article to be pushed off of sortation bed 74in different manners. Divert tracks 34 may be configured, and switches92 may be activated, in the manners described in commonly assigned U.S.Pat. No. 6,041,909, issued Mar. 28, 2000 to James Shearer, Jr., thedisclosure of which is hereby incorporated herein by reference.

At least one slat 80 includes a unique identifier, such as a magneticplate 96 positioned generally near the bottom of the slat (FIG. 6). Theslat with such an identifier defines an index slat 80 a. The magneticplate 96 is detectable by slat sensors 98 positioned underneath slats80. In addition to sensing when the index slat 80 a passes over them,slat sensors 98 are also designed to detect the spaces or air gapsbetween each slat 80 as they pass over the slat sensor 98. Asillustrated in FIG. 9, each slat sensor 98 is connected to an associateddivert control module 52. Each slat sensor 98 sends a signals to itsassociated divert control module 52 when it detects the index slat 80 aabove it, as well as when it detects each gap between each slat 80. Eachdivert control module 52 is provided information on the total number ofslats 80 that make up sortation bed 74. Each divert module 52 uses thisinformation in combination with the signals from slat sensor 98 todetermine which particular slat is above its associated slat sensor 98at any given time. Divert control module 52 does this by detecting theindex slat 80 a and then counting the number of slats that subsequentlypass by slat sensor 98. For example, index slat 80 a may be assigned aunique number, such as the number one. The next slat that passes by isassigned another unique identifier, such as the number two. Eachsubsequent slat may be assigned the next integer number until the indexslat 80 a is once again detected. Divert control module 52 counts howmany slats have passed over slat sensor 98 by counting the number ofsignals it receives from slat sensor 98, which sends a signal each timethe gap between two adjacent slats is detected. By counting the numberof slats that pass by each slat sensor 98, divert control module 52knows what particular slat is above that sensor 98 at any given time.This information is used to determine at what moment in time theelectromagnetic diverter switch or switches 92 that are controlled bydivert control module 52 should be activated, as will be explained inmore detail below.

As noted above, slat sensors 98 may include a conventional Hall effectsensor for detecting when magnetic plate 96 passes by it. In order todetect the gaps between slats 80, slat sensor 98 may also include areluctance sensor that detects when a metallic material comes into closeproximity to a detection head surface on the sensor. Because the slats80 are preferably made of metal, such as aluminum, the reluctance sensordetects the gaps between slats by detecting those instances when noadjacent metal (i.e. no slat) is present. The design of the reluctancesensor can vary within the scope of the invention, and other types ofsensors can be used. Details of one type of reluctance sensor that canbe used with the present invention are found in the published PCT patentapplication assigned international publication number WO 02/26602 A2,which, as noted above, has been incorporated herein.

In addition to slat sensors 98, each divert control module 52 isconnected to, and in communication with, at least one shoe sensor 100,at least one switch sensor 102, at least one divert switch 92, and atleast one article sensor 104. In the specific embodiment of FIGS. 3-9,each divert control module 52 is connected to, and in communicationwith, six shoe sensors 100, one switch sensor 102, four divert switches92, and one article sensor 104. These numbers can be varied.Furthermore, the use of sensors 100, 102, and 104 is optional, and anyone or more of these types of sensors can be omitted from control system70. Divert control module 52 implements the specific communicationsprotocol that is used with each of these sensor and actuators; thespecific voltages, currents, and/or frequencies that must be applied todrive a particular actuator; and the meaning of the electrical signalsthat it receives from the associated sensors. This information is notpassed on in its entirety to the second tier controllers 42. Therefore,if changes in sensors or actuators 46 are made, only the associateddivert control module 52 may need to be modified. This allowsimprovements in individual sensors and/or actuators to be easilyimplemented in a sortation system without having to change largeportions of the control system. In addition to the communicationinformation discussed above, divert control modules 52 also includealgorithms on how to react to various situations that may occur withouthaving to seek instructions from a tier two controller 42. Thisawareness and the particular types of situations this knowledge may beused in is described in more detail below, but generally includes suchthings as the malfunction of one or more switches 92, the improper orfailed diverting of a pusher 72, and other situations.

Shoe sensors 100 are an optional component of tiered control system 70.Shoe sensors 100 may be positioned in the six locations illustrated inFIG. 8. Shoe sensors 100 may be any type of sensor capable of detectingthe passage of a shoe by the sensor. In one embodiment, shoe sensors 100may be Hall effect sensors that detect the transfer assembly 88 of ashoe or pusher 72 as it passes by in either channel 90 or one of thedivert paths 94. One shoe sensor 100 is preferably positioned upstreamof the set of divert switches 92 that is under the control of the samedivert control module 52 that the shoe sensor 100 is in communicationwith. In other words, one shoe sensor 100 is positioned at the upstreamend of a sortation station 30. Another shoe sensor 100 is preferablypositioned at the downstream end of the same sortation station 30. Theremaining four shoe sensors 100 are positioned along divert paths 94 inany suitable location that is downstream of switches 92. With thisarrangement, a transfer assembly 88 about to enter sortation station 30will first be detected by the upstream shoe in path 90. Thereafter, thattransfer assembly will be detected by one of the other five shoe sensors100 before it exits sortation station 30. If no such exiting of thetransfer assembly 88 is detected by any of these five shoe sensors 100,then it can conclude that a malfunction has occurred. Either one of theshoe sensors 100 has failed to detect the transfer assembly 88, or thetransfer assembly 88 has broken away from the rest of the pusher 72 andfallen beneath paths 90 or 94.

Divert control module 52 keeps track of the detection of a transferassembly 88 by the upstream-most shoe sensor 100 in a sortation station30. After the transfer assembly 88 has been detected, divert controlmodule 52 not only checks to see that the transfer assembly 88subsequently exits the sortation station by passing by one of the otherfive shoes sensors 100, but it also checks to see that the transferassembly 88 has passed by the correct shoe sensor 100. For example, ifthe transfer assembly 88 was attached to a shoe 72 that was supposed tobe diverted down the upstream-most divert path 94, then the shoe sensor100 in the upstream-most divert path 94 should detect this transferassembly when it passes by. If it does not detect this transferassembly, but one of the other shoe sensors does, then divert controlmodule 52 knows that the shoe followed an incorrect path. Moreover, byknowing which shoe sensor 100 detects the mis-diverted transferassembly, divert control module 52 will know which particular divertpath 94 or straight path 90 the mis-directed shoe actually traveleddown. Based on the information detected by shoes sensors 100, divertcontrol module 52 takes appropriate action.

The appropriate action will depend upon the particular divert errordetected by shoe sensors 100. If a shoe is detected entering sortationstation 30, but no shoe is detected exiting the station, then the shoeand transfer assembly may very well have been broken. In such a case,divert control module 52 would inform divert manager 62 (a tier 2controller) of the failure. Divert manager 62 may rank this error as aserious error and initiate a shut down sequence for the sortation bed74. Divert manager 62 would inform a system controller—a tier 3controller—of its shut down procedure. Either the tier 3 controller orthe divert manager 62 would inform any controllers upstream of sortationbed 74 that needed to know about the sortation bed's shut down so thatthey could take appropriate action, such as shutting down so thatarticles do not keep getting fed to a non-operating sortation bed 74.Alternatively, the divert manager may instead record the shoe failureand remove that shoe from the list of shoes available for diverting.

If a divert control module 52 detects that a transfer assembly 88 hasmerely been mis-directed down one of divert paths 94 or straight path90, rather than having broken up and disappeared from detection, thenthe divert control module 52 may note this error and send a message todivert manager 62 of the error. Because such an error may not be asserious as a broken shoe and transfer assembly, divert control module 52may continue to divert shoes 72 and the sortation bed 74 may not beshut-down immediately. Divert manager 62 would log the noted error andkeep track of all such errors. Divert manager 62 is programmed to send astatus message to the tier three controller about the noted error sothat it can be communicated to humans via an interface controlled by thetier three controller. Divert manager 62 may also preferably beprogrammed to only initiate a shut-down of the sortation bed 74 if thenumber of mis-directed shoes over a given time period of a particularswitch 92 exceeds a predetermined threshold. The shut down sequencecould also be influenced by information received from article sensor104, as described below.

At least one article sensor 104 may be positioned along each branchconveyor 32 (FIG. 1). Each article sensor 104 may be a conventionalphoto-eye or other type of conventional sensor that detects the presenceof an article as it travels by the sensor on the branch conveyor 32.Each article sensor 104 is in communication with the divert controlmodule 52 that controls the diverting of articles onto the particularbranch conveyor 32 on which sensor 104 is positioned. Thus, each articlesensor 104 sends signals to its associated divert control module 52indicating when an article on branch conveyor 32 is detected. Thisallows divert control module 52 to determine whether an article has beensuccessfully diverted to a branch conveyor 32.

For example, if the divert control module 52 activates one or moreswitches 92 to a diverting state and the corresponding article sensor104 does not subsequently detect the passage of an article on the branchconveyor, then the article was not successfully diverted. The articlemay still be on sortation bed 74, or it may have fallen onto the floor.When divert control module 52 detects this error, it sends a statusmessage of the error to divert manager 62. Divert manager 62 may beprogrammed to log the error and pass a message onto the tier threecontroller to output notification to the human interface controlled bythe tier three controller. Divert manager 62 may also be programmed tokeep track of the frequency of such error messages for each individualdivert module 52. If the package diversion errors occur for a particularsortation station at a particular frequency above a threshold, thendivert manager 62 may initiate a shut-down of sortation bed 74. Forexample, if divert manager 62 detects that two or more articles thatwere to be diverted down a particular branch conveyor 32 aresuccessively mis-diverted, then an article jam or pile-up may haveoccurred that will prevent any further articles from being diverted downthat particular branch conveyor. In such a situation, divert manager 62may be programmed to first check to see if there are any other branchconveyors that are redundant to the blocked branch conveyor beforeinitiating a shut-down.

Redundant branch conveyors are alternative conveyor branches 32 thatwill lead an article to a location in the warehouse or factory which isalso an acceptable destination for the article. For example, a firstbranch conveyor 32 may convey articles to a first loading dock, while asecond branch conveyor 32 may convey articles to a second loading dock.Both the first and second loading docks, however, may load articles ontovehicles that are intended for the same ultimate geographic location,and therefore an article to be diverted down the first branch conveyor32 could also acceptably be diverted down the second branch conveyor 32.If there are any such redundant branch conveyors, divert manager 62stores this information and consults it in the case of a successivearticle mis-diverts on a given branch conveyor. In such a case, divertmanager 62 changes the assigned destinations of all of the articles thatwere otherwise to be diverted down the malfunctioning branch conveyorsuch that they are diverted down one or more of the redundant branchconveyors. In addition to changing the destinations, divert manager 62also informs the tier three controller 40 so that proper notification ofthe malfunction can be communicated to the human operators of thesystem.

Divert control manager 62 may also be programmed to change which branchconveyors 32 an article is diverted down in the case where a branchconveyor is determined to be full of accumulated packages and aredundant branch conveyor is available. Article sensors 104 also detectthis situation. Whenever an article is detected by a sensor 104 for agreater amount of time than would be expected for it to move beyondsensor 104, divert manager 62 determines that that branch conveyor is atleast temporarily full. Divert manager 62 then causes articles intendedfor the full branch conveyor to be diverted down one of the redundantconveyor branches until sensor 104 provides an indication that thepreviously full branch conveyor is no longer full. Thereafter, divertmanager 62 reverts back to diverting articles to the previously fullbranch conveyor in the normal manner.

As noted above, each divert control module 52 is also in control ofdivert switches 92 which are preferably, although not necessarily,electromagnetic switches. In order to determine if each of theseswitches is operating properly, a switch sensor 102 is preferably placedadjacent, such as underneath, each electromagnetic switch 92. Switchsensors 102 may be any conventional sensor, such as a Hall effectsensor, that is able to detect the electromagnetic field created by theelectromagnetic switch 92 when it is activated. Divert control module 52therefore receives feedback from switch sensors 102 regarding thesuccessful or unsuccessful activation of each divert switch 92. Ifdivert control module 52 determines from a switch sensor 102 that aparticular switch 92 has not been successfully energized, it informsdivert manager 62. Divert manager 62 logs this error. Divert manager 62analyzes this log of errors to determine whether the unsuccessfulactivation of a switch is an occasional or isolated incident, or whetherthe errors are generally continuous. In the former case, nothing furtheris done with the possible exception of sending a message to the tierthree controller which may communicate this to the human interface inthe form of a periodic status report, or in any other form. In thelatter case, divert manager 62 concludes that the particular switch 92is inoperative and makes adjustments to the divert commands it sends tothe divert control module 52 for that sortation station 30 in order toaccommodate, to the extent possible, the defective switch 92.

The diverting commands sent from divert manager 62 may take on any form,but preferably are commands to divert pushers on one or more specifiedslats 80. As discussed above, each individual slat 80 is assigned aunique identifier. Commands from divert manager 62 specify which slatsare to have their pushers diverted. These commands also specify which ofthe four divert switches 92 are to be used in carrying out the articledivert and the sequence in which the switches are to be activated. Eachdivert control module 52 has information on the distance between itsassociated slat sensor 98 and each of its four divert switches 92. Usingthis information, divert control module 52 determines when the specificslat or slats identified in the divert command are immediately aboveeach divert switch 92. Divert control module 52 therefore knowsprecisely when each divert switch 92 is to be activated, and the timingof this activation is completely controlled by divert control module 52.Thus, divert manager 62's divert commands do not need to specify aparticular time for activating the divert switches 92, nor do they haveto be sent at the precise moment when switches are to be activated. Thedivert commands merely need to be sent prior to the article arriving atthe particular switch or switches 92 that are to be activated incarrying out the diversion of that article. Each divert control module52 preferably includes a memory queue for retaining a predeterminednumber of these commands so that multiple commands can be sent andretained. Divert control modules 52 are able to remove items from thesequeues based on special commands from divert manager 62. Such commandsto remove or alter divert commands stored in the queue may be generatedin response to divert manager 62's recognition that a particular branchconveyor 32 is blocked, or otherwise unavailable, and that analternative branch conveyor 32 must be used.

The specific commands to divert pushers may identify one or morepatterns of the divert switches 92 that should be activated. One exampleof this is illustrated in FIG. 13. A divert command is illustrated inFIG. 13 that is eight bytes long. The first two bytes identify thespecific slat which will initiate the implementation of the command. Inthis case, the identified slat is a slat that has been assigned theidentification number “2” (binary 10). The remaining digits of thecommand are divided into groups of four bits (nibbles) that specifypatterns for activating the divert switches 92. The zeros in each nibblecorrespond to a non-diverting state of a switch 92 and the onescorrespond to a diverting state of a switch 92. The first nibble afterthe pair of slat identification bytes specifies which of the four divertswitches 92 should be activated at the moment the identified slat hasreached the downstream switch 92 of the sortation station 30. Thismoment is referred to as time 1 in FIG. 13. The most significant bit ofthe nibble corresponds to the upstream-most divert switch 92. The secondmost significant bit of the nibble corresponds to the second mostupstream divert switch 92. The last two bits of the nibble correspond tothe respective last two divert switches 92. Thus, at the moment theidentified slat is over the downstream-most switch 92 (time 1), thisdownstream-most switch will be activated into the diverting state, whilethe remaining three upstream switches will be in the non-divertingstate. The next four bits of the command include a specification ofwhich of the four switches 92 should be activated after the identifiedslat has moved one slat-width downstream of the downstream switch 92 inthe sortation station 30 (time 2). In the illustrated command, only thedownstream-most switch 92 is in a diverting state at this time. When theidentified slat has moved two slat-widths downstream (time 3), none ofthe divert switches will be activated for this time period. In theillustrated example of FIG. 13, an additional seven switch specificationnibbles are included for each moment in time that the identified slathas moved one slat width further downstream. It will be understood thatthe specific number of nibbles that identify divert switch activationpatterns can be varied from that depicted in FIG. 13, and that thespecific command depicted in FIG. 13 is only illustrative. A widevariety of different commands and divert patterns can be sent to thedivert control modules 32 other than the one illustrated. It will alsobe understood that the different time periods illustrated in FIG. 13 arenot necessarily fixed, but are dependent on the speed of the conveyingsurface. Moreover, the illustrated command is based on having fourdivert switches. If sortation stations 30 include a different number ofswitches 92, then the activation pattern for each moment in time willhave a different number of bits. Specifically, the number of bitsdefining each activation pattern will be the same as the number ofswitches. By changing the patterns specified in the divert commands, themanner in which articles are diverted can be controlled. For example, byactivating two switches 92 simultaneously that divert two pushers whichimpact near the front and rear ends of the article, the article will bediverted without rotation. By activating only a single switch to causeone or more pushers to be diverted, the article will be rotated whendiverted. By activating different switches at different times, it ispossible to divert the article with rotation during a portion of thedivert and without rotation during another portion of the divert. Divertmanager 62 determines the manner in which the articles are to bediverted. This decision may be based on the length of the article, itswidth, the absence or presence of articles immediately in front of it orbehind it, the amount of physical separation between it and the trailingor leading articles, as well as the intended destination of the trailingor leading articles. Depending on the length of articles and the numberof activation patterns that are sent in a given divert command, it ispossible to divert more than one article using a single divert command.

Divert manager 62 generates the divert commands that it sends to thespecified divert control modules 52 on the basis of the intendeddestination for the packages or articles traveling on the conveyorsystem. This knowledge of the articles' destinations may be received ina variety of different ways. The tier three controller 40 maycommunicate this information to divert manager 62, for example.Alternatively, divert manager 62 may be in communication with a sensor,such as a bar code scanner, that reads information directly from thearticles themselves about their intended destination. Regardless of howthe destination information is communicated to divert manager 62, divertmanager 62 preferably is in communication with a slat sensor 106 that isupstream of all of the diverting stations 30, yet still on sortation bed74. Divert manager 62 is also in communication with an article sensor108 located on sortation bed 74 upstream of all the diverting stations30 and in a known location relative to slat sensor 106. Using slatsensor 106 and article sensor 108, divert manager 62 determines whichparticular slats an article rests on as it travels on sortation bed 74.By knowing the identity of these particular slats, divert manager 62formulates the appropriate divert commands. As noted above, the divertcommands include the specific slats 80 whose pushers 72 are to bediverted. By knowing the intended destination for an article, as well aswhich branch conveyors 32 will take an article to that destination,divert manager 62 knows which of the divert control modules 52 thedivert command should be sent to. Each divert control module 52preferably includes a unique address that distinguishes it from theother divert control modules. In this manner, divert manager 62 is ableto send commands to specific divert control modules 52.

The addresses of each divert control module 52 may be automaticallyassigned by divert manager 62 upon initial power-up of the system. Onceassigned, divert manager 62 stores this information in memory so thatassignment of the addresses does not need to be performed again exceptwhen a new divert control module 52 is added to the system. Theautomatic assignment of addresses may be carried out by an initial,global command to all divert control modules 52 in the system tellingthem to respond at a specified time. The time for responding may bebased upon the time when index slat 80 a passes by the divert controlmodule 52. By using index slat 80 a as the signal for responding todivert manager 62, the responses of each divert control module 52 willnot interfere with each other. For every response, divert manager 62assigns the responding divert control module 52 an address that issubsequently communicated to that particular divert control module 52.These address assignments remain resident in divert manager 62 and donot need to be communicated to the tier three controller.

An alternative method for initializing each divert control module 52 isto use ultra-wideband (UWB) signals that are emitted from, or detectedby, each divert control module 52. Such signals would be transmitted inconjunction with a plurality of other UWB transceivers that arepositioned within the facility at known locations. From these UWBcommunications, each divert control module 52 could automaticallydetermine its location within the facility, as well as its relativeposition with respect to the other divert control modules 52. Thisrelative location could be determined by direct UWB communications withthe other divert control modules. Once each divert control module 52knows its location with respect to the others, they may automaticallyassign themselves their own unique address based on their positionalorder down sortation bed 74, or some other criteria. Divert manager 62would thus not need to assign addresses, but could instead simplypre-define the position on the sortation bed 74 as having a particularaddress. UWB signals can also be used in control system 70 in any of theways described in commonly assigned U.S. Patent Application Ser. No.60/318,029, filed Sep. 10, 2001, the disclosure of which is herebyincorporated herein by reference.

In addition to the divert control modules 52, divert manager 62 alsocontrols or supervises at least one motor control module 54. Motorcontrol modules 54 control the one or more motors 58 used to powersortation bed 74. While other types of motors may be used, each motorcontrol module 54 preferably controls a linear induction motor 58. Asillustrated in FIG. 9 and is disclosed in International Publication No.02/26602, each motor control module 54 may include a conventional,off-the-shelf linear induction motor driver 110 and an addressableinterface 112. The motor drivers 110 may be standard variable frequencydrives, or other types of drives. The addressable interfaces 112 provideinterfaces to the drivers 110 that allow divert manager 62 tocommunicate with selected motor control modules 54. Each linear motor 58exerts a force on the movable slats 80 by way of a ferrous plateembedded within each slat 80. The amount of force exerted by each motoris controllable by divert manager 62. Divert manager 62 sends commandsto each motor control module 54 instructing the motor control module todrive the associated motor 58 at a particular level. Divert manager 62is also in communication with slat sensor 106 which, in addition toproviding identification of each individual slat, also provides a speedindication. The speed indication is determined by counting the frequencyat which gaps between slats are detected. The width of each slat isknown, as well as the gaps between them, so that the frequency withwhich gaps are detected can be converted into a speed. Divert manager 62sends out commands to each motor control module 54 so that the slats 80of sortation bed 74 move at a given speed. The given speed is chosenbased on information that divert manager 62 receives from the tier threecontroller regarding the desired level of throughput in the overallconveyor system.

Motor control modules 54 may also be in communication with at least onemotor sensor 114. Motor sensor 114 may be a conventional thermistor usedto determine if a particular motor 58 is overheating. The signals fromeach thermistor are transmitted to the associated motor control module54 which interprets the signals, and which has stored the acceptableoperating temperatures for the particular type of motor 58 controlled bymotor control module 54. Based on this information, motor control module54 sends status information to divert manager 62 about the operatingcondition of its motor 58. If motor control module 54 determines thatits associated motor 58 is overheating, divert manager 62 may decreasethe level at which that particular motor is to be driven. In such acase, divert manager 62 is programmed to issue commands to one or moreof the other motor control modules 54 in order to drive those othermotors at a higher level in order to make up for the decreased forcebeing produced by the overheating motor. When the overheated motortemperature has sufficiently fallen, motor control module 54 can commandthe motor to resume its prior level of force production and make acorresponding decrease in the force being produced in the other motors.Divert manager 62 thus determines how each motor 58 will be driven inorder to effect the proper speed of sortation bed 74 while at the sametime varying the loading of each motor, as necessary, in order to keepthem at acceptable operating temperatures. Whenever a motor 58persistently runs at too high of a temperature, divert manager 62 maysend a status message to tier three controller 40 for inclusion indiagnostic reporting that is communicated to the human operators of thesystem.

As discussed above, divert manager 62 contains a variety of differentinformation and intelligence that allows it to deal with various errorsand other situations without having to wait for instructions from tierthree controller 40. These include diverting errors, heating issues withmotors, jammed or blocked branch conveyors, and other situations. Byincluding the intelligence necessary to deal with these situationswithin divert manager 62, tier three controller 40 can be freed fromhaving to address many of the details that it otherwise would have hadto deal with. Moreover, by including such information and intelligencein divert manager 62, modifications to the method of controllingsortation bed 74 can usually be made without having to makemodifications to the tier three controller 40. It will be understood byone skilled in the art that other sensors and/or actuators can be usedbesides those depicted and described herein.

The tiered control system of the present invention can take on a varietyof different architectures, several of which are illustratedschematically in FIGS. 10-12. Each of the architectures includes a plantinformation network 116, which is a network that typical plants andfacilities maintain to monitor the flow of material throughout thefacility. The illustrated architectures are equally viable without sucha network 116. If present, however, the network 116 could be incommunication with a tier three controller 40, as indicated by the linesand arrows in the illustration. The tier three controller 40 would be incommunication with various other components in a manner that depends onthe particular architecture.

In FIG. 10, the tier three controller 40 is in communication with onemerge/induct manager 118, one gapping manager 60 (GM), and one divertmanager 62 (DM). The merge/induct manager 118 oversees the merging andinduction of multiple incoming conveyor lines. It controls the speed atwhich articles on these conveyors are moved, as well as the grouping ofarticles into slugs. Furthermore, it controls the manner in whicharticles from different incoming conveyor lines are merged onto fewerconveyor lines. Gapping manager 60 controls the spacing or gaps betweenarticles after they have been inducted and merged. The divert manager 62controls the diverting of articles on a sortation bed, such as sortationbed 74. This control may be carried out in the manner previouslydescribed.

In the architecture of FIG. 10, tier three controller 40 controls andoversees the operation of managers 118, 60, and 62. Merge/induct manager118 inducts and merges the incoming conveyor lines into a singleconveyor line. Thereafter, the articles traveling on the single conveyorline are properly gapped under the controlled gapping manager 60. Thearticles are then appropriately diverted downstream of that on a singlesortation bed.

FIG. 11 illustrates a cascaded divert control architecture. In thisarchitecture the articles are inducted and merged into a single conveyorline in a manner that is controlled by merge/induct manager 118. Agapping manager 60 thereafter ensures that the articles are properlygapped. Downstream of the gapping manager 60 are three separatesortation beds arranged serially. Each one of these sortation beds isunder the control of a separate divert manager 62. Such separate divertmanagers and sortation beds may be useful where the required physicallength is beyond what can feasibly be manufactured using only a singlesortation bed.

FIG. 12 illustrates a parallel control architecture. In thisarchitecture merge/induct manager 118 inducts and merges incomingarticles down to three separate conveyor lines. Each of these conveyorlines space the articles traveling thereon under the control of aseparate gapping manager 60. Each of the conveyor lines also includes aseparate sortation bed under the control of a separate divert manager62. The parallel diverting architecture of FIG. 12 can be especiallyuseful in increasing the throughput of a diverting system as multiplesortation beds can be sorting articles simultaneously.

The tiered control system of the present invention creates a modularizedcontrol system in which each subsystem is more independent as astand-alone piece than in the past. The subsystems can be functionallytested without the need of interconnection to the main system, therebyallowing for the easy integration of new technologies, modifications inscalability and cost reduction and the more cost-effective making ofsimple repairs. Initial development is also enhanced by the ability toget a subsystem operating that requires less hardware buildup whilemodeling the necessary characteristics of the full system environment.

While the present invention has been described in terms of the preferredembodiments depicted in the drawings and discussed in the abovespecification, it will be understood by one skilled in the art that thepresent invention is not limited to these particular preferredembodiments, but includes any and all such modifications that are withinthe spirit and scope of the present invention as defined in the appendedclaims.

1. A method of controlling a conveyor sortation system comprising:providing a sortation bed having a conveying surface movable in adirection of conveyance; providing an induct conveyor adapted to inductarticles for delivery to said sortation bed; providing a merge conveyorfor merging a plurality of conveying lines; providing a merge and inductmanager adapted to control a speed of said induct conveyor and saidmerge conveyor; providing a first controller adapted to control saidmerge and induct manager; providing a second controller adapted todetermine an article's position on said conveying surface, said secondcontroller responsive to said first controller; providing a plurality ofthird controllers and a plurality of associated divert switches, eachsaid third controller adapted to control an associated divert switch forselectively diverting articles off of said sortation bed; sending anarticle's intended destination from said first controller to said secondcontroller; selecting one of said plurality of third controllers basedon the article's intended destination; and sending an article's locationon the conveying surface from said second controller to said selectedthird controller and instructing said selected third controller todivert said article when said location reaches the associated divertswitch.
 2. The method of claim 1 further comprising: providing a motoradapted to move said conveying surface; providing a fourth controlleradapted to control said motor; and sending a command from said secondcontroller to said fourth controller to cause said motor to operate at aparticular speed.
 3. The method of claim 1 further comprisingdetermining whether any of said divert switches have malfunctioned andsending a message from the associated third controller to said secondcontroller indicating such a malfunction.
 4. The method of claim 2further comprising determining whether said motor has malfunctioned andsending a message from the associated fourth controller to said secondcontroller indicating such a malfunction.
 5. The method of claim 1further comprising providing microprocessors in each of said first,second, and third controllers.
 6. The method of claim 1 furthercomprising providing a plurality of movable slats on said sortation bedand providing a plurality of pushers movable along said slats in adirection generally transverse to the direction of conveyance, saiddivert switches adapted to selectively cause said pushers to move insaid transverse direction.
 7. The method of claim 1 further includingautomatically assigning a communications address to each of saidplurality of third controllers and storing said automatically assignedaddress in said third controllers and said second controller.
 8. Themethod of claim 7 wherein automatically assigning a communicationsaddress to each of said plurality of third controllers includestransmitting an initial command from said second controller to all ofsaid third controllers wherein said initial command causes said thirdcontrollers to respond to said second controller at non-overlapping timeperiods.
 9. The method of claim 8 wherein said non-overlapping timeperiods are defined by reference to movement of said conveying surfaceof said sortation bed.
 10. A conveyor sortation system comprising: asortation bed having a conveying surface movable in a direction ofconveyance; an induct conveyor adapted to induct articles for deliveryto said sortation bed; a merge conveyor for merging a plurality ofconveying lines; a merge and induct manager adapted to control a speedof said induct conveyor and said merge conveyor; a first controlleradapted to control said merge and induct manager; a second controlleradapted to determine an article's position on said conveying surface,said second controller reponsive to said first controller; and aplurality of third controllers and a plurality of associated divertswitches, each of said third controllers adapted to control anassociated divert switch for selectively diverting articles off of saidsortation bed, wherein said first controller is further adapted to sendthe article's intended destination to said second controller and saidsecond controller is further adapted to select one of said plurality ofthird controllers based upon the article's destination and send thearticle's location on the conveying surface to said selected thirdcontroller along with an instruction to said third controller to divertthe article when the article's location reaches the associated divertswitch of the selected third controller.
 11. The system of claim 10wherein said first controller does not maintain information on theposition of any articles on the conveying surface.
 12. The system ofclaim 10 further including a motor and an associated motor controllerfor controlling said motor wherein said second controller is furtheradapted to send a command to said motor controller to cause said motorto operate at a particular speed.
 13. The system of claim 10 furtherincluding a sensor adapted to detect whether any of said divert switchesactually diverted an article off of said sortation bed.
 14. A conveyorsystem comprising: a sortation bed having a conveying surface movable ina direction of conveyance; a plurality of divert switches associatedwith said sortation bed, said divert switches adapted to divert articlesoff of said sortation bed; a plurality of divert modules, each saiddivert module adapted to control at least one of said divert switches; adivert controller adapted to control and communicate with each of saiddivert modules, said divert controller further adapted to transmit anauto-addressing command to each of said divert modules wherein each ofsaid divert modules responds to said auto-addressing command atnon-overlapping times and said divert controller uses the responses ofsaid divert modules to automatically assign a unique communicationsaddress to each of said divert modules.
 15. The system of claim 14wherein said divert modules respond to said auto-addressing command attimes determined by movement of a detectable element associated withsaid conveying surface.
 16. The system of claim 15 wherein saiddetectable element is a magnet moveable with said conveying surface. 17.The system of claim 15 wherein said conveying surface is defined by aplurality of generally parallel slats, each of said slats is associatedwith a unique identifier, and each of said divert modules are able todetermine when a slat having a particular identifier is aligned with aparticular divert switch controlled by said divert module.
 18. Thesystem of claim 15 further including a controller in communication withsaid divert controller, said controller adapted to be able to determinean article's intended destination and communicate said intendeddestination to said divert controller wherein said divert controlleruses said intended destination to determine which of said divert modulesto send instructions to in order to divert the article so that itreaches its intended destination.
 19. The system of claim 18 whereinsaid controller does not send commands to any of said divert modules.20. The system of claim 14 further including a motor and an associatedmotor controller for controlling said motor wherein said divertcontroller is further adapted to send a command to said motor controllerto cause said motor to operate at a particular speed.
 21. The method ofclaim 1 further including: providing a gap manager adapted to controlspacing between articles delivered to said sortation bed; andcontrolling said gap manager with said first controller.
 22. The systemof claim 10 further including a gap manager adapted to control spacingbetween articles delivered to said sortation bed wherein said firstcontroller is adapted to control said gap manager.